Chalcogenides-based dual-band tuning for changing resistance states of reconfigurable intelligent surfaces of devices

Reconfigurable intelligent surfaces are specifically designed manmade surfaces of electromagnetic material, referred to as metamaterial, that are electronically controlled with integrated electronics. Metamaterials are artificially engineered materials fabricated using a stack of metal and dielectric layers. These thin two-dimensional metasurfaces can tune an electromagnetic wave's key properties, such as amplitude, phase, and polarization, as the electromagnetic wave is reflected or refracted by the surface. In other words, a reconfigurable intelligent surface is a two-dimensional surface whose surface can be electronically altered such that it changes the characteristics of any incoming electromagnetic wave, including the wave's phase.

Each metasurface typically is made up of (possibly up to) hundreds or thousands of unit-cells, and because the individual unit-cell can be controlled, reconfigurable intelligent surfaces can provide programmable and smart wireless environments. For example, one scenario is to use such a surface to intelligently reconfigure wireless communications. More particularly, objects in the path of a wireless signal, such as buildings and trees, can block wireless communication signals at higher frequencies, such as millimeter-wave frequency bands (24.5 GHz-52.6 GHz), which are expected to move upwards to sub-terahertz bands as described herein. This can be overcome by installing a large number of base stations to provide coverage to otherwise blocked areas, but doing so would increase the infrastructure costs many times. Instead, a relatively inexpensive metasurface can be installed at various locations to reflect and/or refract higher frequency signals to otherwise blocked or weak coverage areas.

Various ways to control reconfigurable intelligent surfaces have been implemented, including those based on switching technologies such as field-effect transistors (FETs) and PIN diodes (formed from a p-type semiconductor, an undoped intrinsic region and an n-type semiconductor). With such switches used in each unit cell, the wireless operating frequency is a major factor because each of these existing switch technologies has different maximum operating frequencies and other frequency-dependent characteristics. For wireless communications beyond fifth generation (5G), such as 6G's sub-terahertz bands and even future terahertz bands, switch technologies like PIN diodes and FETs are not suitable. Further, with these technologies, switch size factors, ON-state series resistance, and overall power consumption (e.g., PIN diodes require continuous power when in an ON state, and there can be hundreds or thousands of unit cells) are also significant drawbacks.

Various aspects of the technology described herein are generally directed towards phase-change material-based (e.g., chalcogenide-based) radio frequency components, and more particularly, a multi-state tunable capacitive element coupled to a dual split ring capacitive device for reconfigurable operation. The technology described herein facilitates a practical reconfigurable intelligent surface for wireless communication frequencies currently in use as well as those wireless communication frequencies planned for advanced networks beyond 5G.

More particularly, a nested-split-ring resonator design of a reconfigurable intelligent surface is described using chalcogenide phase-change material-based radio frequency components for achieving dual-band multi-state capacitive tuning, e.g., at 28 GHz and 110 GHz with massive bandwidth of 5 GHz. The example capacitor values chosen in this design are well within a reasonable practical implementation tolerance range that can be implemented on any substrate such as opaque/transparent, solid/flexible or any other material. The dual-band approach at 28 GHz and 110 GHz makes this device usable for mm Wave 5G and 6G applications, including simultaneous operation at both frequencies, to enhance the coverage. The size of the proposed panel need not be larger than a few cm but can be scaled up or down to achieve desired beamforming performance.

As will be understood, actuation voltages or currents programmatically applied to phase-change material can toggle the phase-change material between lower and higher resistance states. When such (e.g., chalcogenide) elements are arranged in a capacitive circuit, different effective capacitance values can be realized to control a change in the phase of reflected or refracted electromagnetic waves. Indeed, analog-like fine tuning of capacitance can be achieved by controlling the states of such a capacitive device.

It should be understood that any of the examples herein are non-limiting. As one example, chalcogenide materials, e.g., alloys based on germanium-antimony-tellurium (GeSbTe), are described and evaluated as one very suitable phase change material for use in multi-state tunable capacitive elements; however, this is only one non-limiting example, and other materials, including those not yet developed, can be leveraged by the technology described herein. Thus, any of the embodiments, aspects, concepts, structures, functionalities or examples described herein are non-limiting, and the technology may be used in various ways that provide benefits and advantages in communications and computing in general. It also should be noted that terms used herein, such as “optimize” or “optimal” and the like only represent objectives to move towards a more optimal state, rather than necessarily obtaining ideal results.

Reference throughout this specification to “one embodiment,” “an embodiment,” “one implementation,” “an implementation,” etc. means that a particular feature, structure, or characteristic described in connection with the embodiment/implementation can be included in at least one embodiment/implementation. Thus, the appearances of such a phrase “in one embodiment,” “in an implementation,” etc. in various places throughout this specification are not necessarily all referring to the same embodiment/implementation. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments/implementations.

The following detailed description is merely illustrative and is not intended to limit embodiments and/or application or uses of embodiments. Furthermore, there is no intention to be bound by any expressed or implied information presented in the preceding sections, or in the Detailed Description section.

One or more embodiments are now described with reference to the drawings, wherein like referenced numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a more thorough understanding of the one or more embodiments. It is evident, however, in various cases, that the one or more embodiments can be practiced without these specific details.

Further, it is to be understood that the present disclosure will be described in terms of a given illustrative architecture; however, other architectures, structures, substrate materials and process features, and steps can be varied within the scope of the present disclosure.

It will also be understood that when an element such as a layer, region or substrate is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements can also be present. In contrast, only if and when an element is referred to as being “directly on” or “directly over” another element, are there are no intervening element(s) present. Note that orientation is generally relative; e.g., “on” or “over” can be flipped, and if so, can be considered unchanged, even if technically appearing to be under or below/beneath when represented in a flipped orientation. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In contrast, only if and when an element is referred to as being “directly connected” or “directly coupled” to another element, are there no intervening element(s) present.

Reference in the specification to “one embodiment” or “an embodiment” of the present principles, as well as other variations thereof, means that a particular feature, structure, characteristic, and so forth described in connection with the embodiment is included in at least one embodiment of the present principles. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment,” as well any other variations, appearing in various places throughout the specification are not necessarily all referring to the same embodiment. Repetitive description of like elements employed in respective embodiments is omitted for sake of brevity.

Aspects of the subject disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which example components, graphs and/or operations are shown. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. However, the subject disclosure may be embodied in many different forms and should not be construed as limited to the examples set forth herein.

A planar implementation approachof the chalcogenide elements for the described technology is disclosure is shown in. In, contactsandare depicted above metallization componentsand, respectively. A thermal barrieris shown above the chalcogenide material, which in turn is above a thin insulation layer. An actuation mechanismthat outputs heat energy based on voltage or current pulses as described herein melt and quench the chalcogenide materialthrough the insulation layer, which when applied can change the state of the chalcogenide material.

The actuation mechanismis further contained by another thermal barrier, which is atop a dielectric substrate. A bottom metallization stripis below the dielectric substrate.

Phase change (chalcogenide) material is formed with alloys containing group VI elements such as sulfur (S), selenium (Se) and/or telluride (Te). Among these, the germanium-telluride (GeTe) alloy is generally the most popular for radio frequency and optical memory applications. Phase change material has a property of reversibly switching between amorphous and crystalline states upon specific heat treatment by controlled electrical pulses. The state in which atoms are arranged in a disorderly manner (short range order) is called the amorphous state, whereas the state where atoms are organized in an orderly manner (long range order) is called the crystalline state. The disordered amorphous state has a lower mean free path of conduction for electrons that impedes current flow due to electron scattering, thus resulting in a higher resistance state when compared to the crystalline state.

As shown in, a medium amplitude (typically 1-2 V for a voltage pulse) and relatively longer duration (typically on the order of 100 nanoseconds) SET electrical pulse (e.g., represented in the left portion of the actuator) is used for crystallization during a transition to the ON state. Energy from the SET pulse heats the material for sufficient time to crystallize the material and provides adequate time for atoms to reorganize to an orderly arrangement, thus transforming from an amorphous state to crystalline stateL. To change to the amorphous state, a short duration (typically less than 100 nanoseconds) and high amplitude (typically >2 V for a voltage pulse) RESET electrical pulse is used. The RESET pulse provides sufficient energy to melt the material to disorder the atoms followed by rapid quenching to freeze the atoms, thus transforming the material from the crystalline state to the amorphous stateH. Significantly, only a short duration pulse is required to switch the state of the material between states; the pulse transforms the material and latches the material into the state, without the need for continuous power in either state. The pulse duration and amplitude can be further optimized by tuning the ratio of GeSbTe alloy ratios.

The technology described herein can be based on a metal-insulator-metal capacitorthat significantly improves (relative to a conventional metal-insulator-metal capacitor) the self-resonant frequency and quality factor (Q-factor) while keeping the capacitor value constant, as described in U.S. patent application Ser. No. 17/934,701. This provides an ultrahigh frequency metal-insulator-metal capacitor. As represented in, an example of such a ring capacitoris provided with distributed interconnectsaround the desired overlap area periphery of the two overlapping conductorsandwith a dielectric. The interconnectshave vias through the dielectric medium. RF ports (collectively) includes an RF signal portand RF ground port(s)() and(). A substrateis shown underneath the other components. Note that in general, this capacitor design is independent of dielectric thickness, permittivity, and/or overlapping area.

Such a capacitor can be built with straightforward design modifications relative to a conventional capacitor, including extending the top conductor electrode to cover a portion of the RF ground plane. This, along with the distributed array of interconnects and their associated vias, provides more optimal surface current density.

As can be readily appreciated, the ultrahigh frequency capacitor can be used with any arbitrary shape of MIM capacitor, not only a circular overlapping area but other shapes, e.g., rectangular, including a dual nested split ring capacitor as shown in. Further, the technology described herein can be used on standard two-layer MIM capacitors that include two metal conductor electrodes, as well as in multilayer MIM capacitors, which can potentially include multiple metal conductor layers (e.g., a third conductor and a second insulator) to reduce the overall area of the device.

shows an example design of a unit-cell, including a dual split-ring type resonator formed by thin film metallization componentsand, with nested thin film metallization componentsand. The dual split-ring type structure is formed on the top metal layer which is separated from the bottom metal stripby a high permittivity dielectric substrate. The phase reconfigurability is achieved by using a chalcogenide, non-volatile multi-state tunable capacitor. Different reflection phases can be obtained by actuating a desired capacitance value or using a combination of capacitance values integrated within the unit cell.

shows the unit-cellwith the contactsandthat couple the chalcogenide, non-volatile multi-state tunable capacitorto the thin film metallization componentsand. The contactsandthus integrate the non-volatile multi-state tunable element into the unit cellinside the periphery of the outer split ring capacitor pair (componentsand). Note that although not explicitly depicted, it is feasible to have another non-volatile multi-state tunable element inside the periphery of the inner, nested split ring capacitor (componentsand), which may provide for additional tuning capabilities.

The technology described herein thus provides a unit-cell devicefor very high frequencies that can be used for 5G, 5G-advanced and 6G applications, including millimeter wave capacitance change with zero static DC power consumption. The reconfigurability of the unit cell is achieved by integrating the chalcogenide multi-state tuning capacitor elementwith outer the split-ring (componentsand). In one implementation, the size of the tunable elementis smaller than 0.2×0.2 mm, thus making this technology a viable choice for highly miniaturized reconfigurable intelligent surface panels. For example, an array of these reconfigurable intelligent surface panels can be used to enhance outdoor wireless communications coverage as well as for indoor radio coverage enhancement. Depending on the choice of substrate, such reconfigurable intelligent surface panels can be developed on opaque materials, or transparent materials, e.g., to install on windows.

The multi-state tuning is achieved by integrating metal-insulator-metal capacitors or any other type of capacitors which can be developed using just two metal layers on a substrate, and integrating one or more chalcogenide switches, each having two states, a lower resistance state and a higher resistance state. A single switch is sufficient for two phase changes of a unit cell, e.g., zero or 180 degrees. However, as described herein, a circuit formed by a number of subcircuits can be used to implement analog-like tuning.

One example circuitfor the tunable chalcogenide device is shown in, with the contactsandbeing accessible for coupling to the split-ring resonator as in. In one implementation shown in, the switches S-Sn are in series with the capacitors C-Cn. Each chalcogenide switch can be independently actuated for a resistance change between the higher and lower resistance states with the application of a short actuation pulse of low voltage and a few nanoseconds time period, as described herein with reference to.

The performance of each switch is dictated by a shunt capacitor Cp as shown in. The value of Cp can be reduced in various known ways. The Ls in each subcircuit is the series inductance between the chalcogenide switch and the capacitor Cn.

Each switching element is changeable between higher and lower resistance states. The capacitor values C-Cn can be arranged to provide “n”-states with 2increasing capacitive branches from Cto Cn.

The capacitance states can be implemented as a 2succession. For example, if C=0.1 pF, then the first state will be C(1×C=0.1 pF), C(2×C=0.2 pF), C(4×C=0.4 pF), C(8×C=0.8 pF), . . . . Cn (2n×C=C*2pF) and so on.

For practical implementation, the examples herein are directed to reasonable values of capacitance to keep the self-resonant frequency of the capacitors away from the design bandwidth of 12 GHz around center frequency 28 GHz and center frequency 110 GHz. The capacitance C can be scaled to a lower value to have more precise control and have more stages, or on the other hand can have larger steps with higher initial C values. To obtain analog-like tuning from this digital step approach, a step value of C=0.1 pF is reasonable to implement on various substrates.

For C=0.1 pF, a chalcogenide switch connected to the respective branch can be actuated to add to the total capacitance of that branch. For example, if in one example design, the device is 4-bit, whereby 16-stage tuning can be achieved by either actuating the switches corresponding to an individual bit or a combination of two or more bits, such as C(0.1 pF), C(0.2 pF), C+C(0.3 pF), C(0.4 pF), C+C(0.5 pF), C+C(0.6 pF), C+C+C(0.7 pF), C(0.8 pF), C+C(0.9 pF), C+C(1.0 pF), C+C+C(1.1 pF), C+C(1.2 pF), C+C+C(1.3 pF), C+C+C(1.4 pF), or C+C+C+C(1.5 pF).

From the example of 4-bit tuning, a bit or combination of bits can provide 0.1 pF of step size, which can be reduced by scaling the lowest capacitor, or by increasing from a 4-bit to 5-bit approach. With respect to a single tunable element, the phase precision comes without increasing the complexity of the design. Unlike some PIN diode-based designs, there is no need to add multiple elements to achieve more than two phase states. Further, most commercially available varactors, PIN diodes, or semiconductor switches require constant voltage in the steady state; in contrast, the chalcogenide switches described herein do not require any power to hold either state. When these elements are used in an array of hundreds or thousands of unit-cells, the power saving is exponential.

The device performance can be simulated using full-wave 3D electromagnetic (EM) simulation software, and the phase shift offered to the reflected signal can be evaluated for a discrete set of capacitance states of the chalcogenide capacitance, which can be electronically controlled. One example unit-cell was designed for simultaneous operation in each band around center frequencies 28 GHz and 110 GHz, which is the set of operational frequencies for 5G networks and advanced networks, including future 6G networks. The relative phase shifts offered to the reflected signals from the unit-cell is graphically represented in, with the minimum tuning states corresponding to the lower end of the chalcogenide tunable capacitance range, and the maximum tuning states corresponding to the higher end of the capacitance range. The x-axis is truncated between 35 and 110 GHz to better visualize the tuning performance of the device.

For an application in which only two different phase shift states are needed, chalcogenide switches can be used instead of varactors, however as described herein, the technology facilitates much more granular control, and thus more phase shift options, when needed.shows the shift in the resonance frequency by evaluating the magnitude of S-parameters of the unit-cell, further confirming the phase shift achieved from the device. The device is designed to operate over 25 to 30 GHz (Band 1) with 28 GHz center frequency and simultaneously over 107 to 112 GHz (Band 2) with 110 GHz center frequency without change in dimensions and with same actuation method of the chalcogenide switching elements. The simulations were carried out using finite element modeling; The simulations were not circuit model simulations but rather full three-dimensional field electromagnetic simulations considering the majority of the parasitic elements and the relevant bias network.

A reconfigurable intelligent surface can be formed by arranging multiple unit-cells in a two-dimensional m×n array, such as shown in the latticedepicted in. An example 8×8 array of unit-cells is shown in the top view () of the lattice structure surface.shows a bottom view representation of the surface; the bottom metal strips()-() are visible in this bottom view.

As previously seen from the above-described performance graphs, each unit-cell can alter the phase, hence bend, an impinging electromagnetic wave and redirect the wave in the desired direction. The redirection of larger reflected waves can be controlled by synchronizing the phase shift from a group of unit-cells and creating patterns of constructive and destructive interference. This interference pattern reforms the incident beam and sends it in a particular direction determined by the pattern. Such orchestration of phase shift from individual unit-cells can be controlled in a reconfigurable intelligent surface configuration via a field-programmable gate array (FPGA) controller or the like. To determine the reconfigurable intelligent surface configuration in dynamic real-life environment, a set of predefined reference signals (known to both transmitter and receiver) are sent from the base station and the channel impulse response is determined.

show how the phase shifts from the unit-cells are configured such that a constructive interference of the reflected signals from each unit-cell is achieved in the desired target direction. Destructive interference to a desired direction can also be leveraged.

As shown in, the overall reconfigurable intelligent surface system showing the direction of the reflected beam/electromagnetic wave is intelligently controlled with phase shift by the configuration, in this example via a field-programmable gate array. With respect to configuring the array digitally, a field-programmable gate array controlleris used to provide the output, mapped to a cell and converted (block) to the appropriate RESET or SET pulse based on the zero- or one-bit pattern instruction as needed, to each cell of the array of cells. The output gives instructions to the individual switching elements of the individual unit-cells, independent from each other switching element, and sets the cell's capacitance independent from each other cell. Actively tuning the phase change material-based (GeTe) varactors in each cell can be individually controlled by the field-programmable gate array, which provides a coding output of 0s and 1s.

Unlike other reconfigurable intelligent surfaces (in which each unit-cell typically can only provide either a phase response of 0° or 180°; the coding for such a 1-bit digital cell state will be either “0” or “1” for OFF and ON switching, respectively), the analog-like reconfigurable intelligent surface described herein can use higher bit coding to describe the phase responses from individual unit-cells. Depending on the beam steering precision desired by a given application, a system can select the number of phase states needed. For example, a 1-bit system can provide 2 possible phase states (chalcogenide switches can be used) while as described above, a 4-bit system can provide 16 different phase state possibilities (e.g., the tunable chalcogenide capacitor as described herein) from each cell.

The technology described herein can function with a minimal power supply, as the electrical pulse is needed only during a change of configuration, a significant advantage over technologies that need continuous power to hold one of the states. Another significant and beneficial feature of this design is that the unit cells described herein can receive and transmit electromagnetic waves simultaneously, hence achieving full-duplex operation.

The technology described herein is suitable for reconfigurable intelligent surface-assisted wireless communications. Because the direct path between the access point and a target of interest can be fully/partially obstructed by other objects, the use of a reconfigurable intelligent surface can substantially improve the wireless network performance, particularly in crowded indoor/outdoor scenarios.

For example, with respect to an outdoor scenario, by installing the reconfigurable intelligent surface on common surfaces such as building walls, windows, billboards, traffic signs and the like, and because as described herein the direction of the reflected and/or refracted beams can be controlled, including remotely controlled, reasonably optimal reconfigurable intelligent surface deployment positions can be identified, along with the corresponding size of the reconfigurable intelligent surface needed. Reconfigurable intelligent surface placement and size can be in conjunction with the planning for a base station's position, or done afterwards by identifying the blind areas of poor signal strength in the network coverage map. This can not only improve the signal reception in the shadow areas, but also improve the data rates in the areas with an already good signal reception. Thus, a reconfigurable intelligent surface can be used for solving the network coverage problem of 5G/6G and even beyond, without adding much power/cost overhead.

Consider by way of example a typical scenario of an outdoor urban area with a single base station. For low frequency radio transmissions, the signal can propagate to long and far distances without significant attenuation due to its long wavelength. But high frequency signals suffer serious attenuation and blockage from objects, whereby the wireless coverage from a single base station will be weak, or even provide no coverage in certain zones. Depending on the location of the base station and the positions of the users, the (mostly) optimal location and size for reconfigurable intelligent surface on billboards, highway signs, walls, windows, and corners of the buildings can be selected.

The signals from the base station reflect off of (or can be refracted by) the passive reconfigurable intelligent surface, can be steered in the direction of most users, and also can be steered to other reconfigurable intelligent surface in the area for further reflection/refraction. The users close to the base station generally receive a direct path signal from the base station, and (likely) also receive a reflected signal from a reconfigurable intelligent surface. The users further away from the base station (or behind obstructions) can receive the reflected or refracted signals from one or multiple reconfigurable intelligent surfaces. One or more of the reconfigurable intelligent surfaces also can employ amplification to boost signals if and when appropriate.

In an indoor scenario, windows and walls can be covered with reconfigurable intelligent surface films, which can be generally transparent, in order to extend wireless coverage indoors. By locating such films on the windows, the signals coming from the outside can be refracted and boosted inside the building, enhancing the coverage inside. The signals to an illegitimate user, e.g., an eavesdropper, can be blocked by destructive interference.

One or more aspects can be embodied in a capacitive device, such as described and represented in the examples herein. The capacitive device can include a first capacitor having a first capacitance value, the first capacitor comprising a first conductor, a second conductor, and dielectric material between the first conductor and the second conductor and a second capacitor having a second capacitance value, the second capacitor comprising a third conductor, a fourth conductor, and the dielectric material between the third conductor and the fourth conductor. The capacitive device further can include a tunable capacitive device configured to selectively adjust the first capacitance value of the first capacitor of the capacitive device to a first different capacitive value from the first capacitance value and the second capacitance value of the second capacitor of the capacitive device to a second different capacitive value, the tunable capacitive device comprising a first contact coupled to the first conductor and a second contact coupled to the second conductor, and further comprising a capacitive circuit, the capacitive circuit comprising a switching element comprising phase change material that changes to a lower resistance state when heated by a first energy pulse, and changes to a higher resistance state when heated by a second energy pulse that is different from the first energy pulse, the switching element being coupled to a third capacitor to couple the third capacitor to the capacitive circuit, and decouple the third capacitor from the capacitive circuit, based on whether the phase change material is in the lower resistance state or in the higher resistance state. The capacitive device further can include a controllable energy transfer component that selectively transfers first heat to the phase change material via the first energy pulse to change the phase change material to the lower resistance state, and transfers second heat via the second energy pulse to the phase change material to change the phase change material to the lower resistance state.

The first capacitor can include a first split-ring resonator capacitor, the second capacitor can include a second split-ring resonator capacitor, and the second split-ring capacitor can be nested within the first split-ring capacitor.

The first capacitor can include a first split-ring resonator capacitor, the second capacitor can include a second split-ring resonator capacitor, and the first split-ring capacitor can be nested within the second split-ring capacitor.

The first capacitor can include a distributed array of conducting interconnects.

The capacitive device can be incorporated into a unit cell of a reconfigurable intelligent surface. The capacitance value of the capacitive device can be variable to control a first phase shift of a first frequency, and a second phase shift of a second frequency that is different from the first frequency, reflected by the unit cell. The unit cell can be part of a group of reconfigurable unit cells that are collectively arranged into the reconfigurable intelligent surface.